The results of recent measurements of the viscosity and thermal conductivity of argon have shown the importance of studying these transport phenomena over a large density range in different regions of the reduced temperature. It appears that the Chapman‐Enskog theory cannot give an adequate description of the new experiments. It has not yet been possible to give a full account of the observations. However, a less rigorous theoretical discussion demonstrates the relevant physical features of the problem. For the moment it serves to indicate a new experimental program. This research may contribute to a more clear understanding of the transport properties in different states of a material, including the difficult intermediate region between the gas and liquid state.